Low capacity high temperature coaxial cables



1 A. BoNDoN 2,740,826

LOW CAPACITY HIGH TEMPERATURE COAXIAL CABLES April 3, 1956 Filed July 9, 1952 INVENTOR BCN DON LEWBS A.

ATTORNEYS United States PaterrtY G LOW CAPACITY HIGH TEMPERATURE COAXIAL CABLES Lewis A. Bondon, Arlington, N. J., assignor to Product Development Company, Arlington, N. .5., a corporation of New Jersey Application July 9, 1952, Serial No. 297,887

3 Claims. (Cl. 174-28) This invention relates to electrical coaxial cables and has more particlar reference to low capacity, high temperature coaxial cables having a considerable degree of ilexibility.

One object of the present invention is to provide a novel and improved low capacity, high temperature coaxial cable particularly designed for low capacity, high and low temperature performance and having a high degree of flexibility.

Another object of the invention is to provide an irnproved low capacity, high temperature coaxial cable, as characterized above, having an outer metal sheath which is flexible, pressure tight, impervious to gasoline, moisture fungus, etc., light Weight, and one which will provide high and low temperature performance and physical protection for the cable core.

Another object of the invention is to provide an irnproved low capacity, high temperature coaxial cable, as characterized above, having a core designed to give low capacity, high temperature and high dielectric strength, and so fabricated that lowest possible attenuation and shunt capacitance is obtained, yet possessing adequate physical properties.

Another object of the invention is to provide an improved low capacity, high temperature coaxial cable, as characterized above, in which the core is made up of interlocking shell-type insulators which allow air to be used as the major portion of the dielectric medium between inner and outer conductors and which permit the cable to be liexed without exposure of the inner conductor, this eliminating any possibility of short circuits which migh occur between inner and outer conductors.

A further object of the present invention is to provide a novel and improved low capacity, high temperature flexible coaxial cable, as characterized above, which is simplified in construction, efficient in operation, and one that is readily adaptable to standard conductors.

Other objects and advantages of the invention will appear in the following specification when considered in connection with the accompanying drawing, wherein:

Fig. l is an elevational view, with parts broken away, of a low capacity, high temperature coaxial cable constructed in accordance with the present invention and showing the manner in which the cable may be connected to a standard military type PL-259A connector;

Fig. 2 is a horizontal sectional view, taken on the line 2 2 of Fig. 1;

Fig. 3 is a vertical sectional view, taken on the line 3-3 of Fig. 2; and

Fig. 4 is a perspective view of one of the insulators shown in Fig. 2.

Referring now to the drawing, there is shown, in Figs. l and 2, a low capacity, high temperature coaxial cable constructed in accordance with the present invention and comprising an outer circular tubular conductor 10; an inner wire conductor 11, and an articulate core, indicated generally at 12 and formed of interlocking shell type insulators 13, which holds the inner and outer conductors generally in concentric relation throughout their lengths.

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The outer conductor 10, preferably, and as shown, is made of a seamless bronze tube which .forms a sheath for the core and inner conductor. The thin side wall of the tube may be formed in a sinuous shape, as shown, to give the tube maximum flexibility.

The inner conductor 11, preferably, and as shown, is made of copper weld wire.

The core 12 is made up of a series of hollow interlocking shell type insulators 13, through which the inner conductor is threaded.

The insulators 13, preferably, and as shown, are made of polytetrauoroethylene. The insulators are identical in construction and each is moulded to the particularshape shown in Pigs. 2 and 4. Each insulator is formed with a hollow open-ended cylindrical portion 14 connected to a hollow generally spherical portion or ball 15 by an intermediate cylindrical neck portion 16. A cylindrical bore 17 extends from'the inner wall of the spherical end portion 15 of the insulator through the neck portion 16 and into the cylindrical portion 14 to about its midsection, where its diameter is widened to a diameter slightly less than the diameter of the spherical portion to form a socket 18 for the ball of the'succeeding insulator. The bottom of the socket 18, at its juncture with the bore, is rounded, as shown at 19, and an arcuateshaped circumferential recess 20 is formed therein by the insertion of the ball and maintained by the radial pressure of the shell, due to the electric memory property of polytetrauoroethylene (see Fig. 2). 'Ihe outer wall of the ball 15 is provided with a small opening 21 through which the inner conductor is threaded.

In assembling the cable, the wire inner conductor is threaded through the insulators 13 which are then joined together by forcing the ball of each insulator into the socket in the next preceding insulator, as shown in Fig. 2; then, the core, with the inner conductor threaded therethrough, is inserted in the outer conductor or sheath 10.

In connection with the foregoing, it will be noted that, due to the unique design of the insulators, the cable may be flexed without pulling the insulators apart and without exposing the inner conductor, thereby eliminating any possibility of shorts which might occur between the inner and outer conductors. This construction of the core also provides a continuous sheath of dielectric, thus insuring high dielectric strength, while, at the same time, allowing air to be used as the major portion of the dielectric medium between the inner and outer conductors. This latter principle, together with the minimum amount of contact which the insulators make withthe inner conductor, insures a low capacity of the cable.

The construction of the sockets permits the balls to be readily inserted therein (a push lit being required) and restrains them from pulling apart. A force of approximately 13 oz. is required to pull the ball from its socket. The ball, portion of the insulators will allow a bending radius of approximately 11/2" without undue stress added to the shell.

As hereinbefore stated, the insulators 13 are preferably made of polytetrauoroethylene because of its following pertinent properties:

(1) Very low capacity f (2) vHigh dielectric strength (3) High temperature performance (4) Low temperature performance (5) Good lexure properties (6) Low attenuation (7) Simplified construction From the properties of polytetratluoroethylene it is noted that the dielectric constant is 2.05. However, the construction of the cable core for the coax Vunder consideration has an effective dielectric constant of 1.21.

The temperature'diiferential to which the core may be subjected without detrimental effects is 65 C. to +200 C. 'Ihese valuesare conservative, and the core in general may be exposed to a greater differential temperature change withoutaffecting to any appreciable extent its electrical or mechanical properties.

As hereinbefore stated, the outer conductor 10 is preferably made of seamless, bronze tubing having a thin sinuous-shaped side wall. An outer conductor of this construction is light in weight, assures pressure-tight construction and physical protection for the cable core, provides for high and low temperature performance, is impervious to gasoline, moisture fungus, etc., and is easily assembled to standard type connectors, as shown in Fig. l, where the connector is indicated generally at 22.

A low capacity, high temperature coaxial cable constructed in accordance with the foregoing and in which the inner conductor was #28 AWG copper weld wire, the outer conductor a seamless bronze tube with a sinuousshaped side wall having an inner diameter of .250" and an outer diameter of .420i.010" and the insulators were made of polytetrafluoroethylene with an outer diameter of .219"i.002 with the overall weight of the cable being .136 lb. per foot, had the following character istics:

Initial capacity 6.5 mmfg/ft.

Capacitance stability 65 C. to +200" C.

Total deviation after cycling 0.77%.

Maximum deviation 0.93% at +200 C.

Corona initiation voltage 2600 volts R. M. S. 60 cycles Corona extinction voltage 2200 volts R. M. S. 60 cycles Dielectric strength greater than 3000 .volts R. M. S. 60

cycles Heat aging 200 C. passed.

Cold bending 65 C. passed A cable such as the foregoing can be fabricated in lengths up to 30 to 35 feet and may be cut in the field by the use of a pipe cutter which provides a clean, accurate cut and leaves no burrs or chips.

From the foregoing, it readily will be seen that there has been provided a low capacity, high temperature coaxial cable which is flexible, light in weight, impervious to gasoline, moisture fungus, etc., simple in construction, easily assembled to standard connectors, and one which tenuation, and high and low temperature performance.

Obviously, the invention is not restricted to the particular embodiment thereof herein shown and described.

What is claimed is:

l. A low capacity, high temperature coaxial cable comprising a flexible tubular outer conductor; a flexible inner conductor; and a hollow ilexible insulating core mounted within the outer conductor, and through which the inner conductor is threaded, for holding the two conductors in generally concentric relation, said insulating core being formed of a plurality of hollow elongated generally cylindrical insulating members each having a socket formed within its bore adjacent one end and with its other end formed in the shape of a ball adapted to be received in the socket of the next preceding member, with the socket substantially embracing the ball and normallyretaining it therein, the construction and arrangement being sucli vthat said core is capable of being subjected to temperatures of at least 200 C. without detrimental effects and of being ilexed without exposing the surface of s'aid inner conductor and engaging said inner and outer conductors at longitudinally spaced points, thus permitting air to be used as the major portion of the dielectric medium be' prising an outer conductor made of a seamless metal tube rhaving its side wall formed in a sinuous shape to` give it `flexibility and resistance to crushing; a core mounted within the outer conductor, said core being formed of la plurality of hollow elongated insulating members made of polytetrauoroethylene, each of said members being generally cylindrical and having a socket formed within its bore adjacent one end and with its other endformed in the shape of a ball, adapted to be received and normally retained in the socket of the next preceding member with the socket substantially embracing the ball whereby the core will be ilexible; ancla wire inner conductor threaded through said insulating members.

References Cited inthe file of this patent UNITED STATES PATENTS 

